With the diversity of radio communication devices possessed by users, it is becoming possible to send e-mail from radio communication devices, use the Internet and exchange data at offices, on street corners, in transport vehicles during movement, or the like. The existence of infrastructure is a prerequisite for these radio networks. On the other hand, an ad hoc network has begun to attract attention which does not require infrastructure, in which a radio communication device performs communication by constructing networks temporarily with radio communication devices scattered in neighboring areas. The ad hoc network is a system which enables communication using a multiple step connection via several radio communication devices when a radio communication device cannot communicate with the desired radio communication device directly, and a problem is what route the radio communication device should take to forward data to the destination radio communication device.
As a route discovery method in a conventional ad hoc network, when a communication request takes place in the radio communication device, there is “The Ad hoc On Demand Distance Vector” method (hereinafter, referred to as “AODV” method) which starts a route discovery in the case that the device does not have route information to the destination, and thereby acquires the shortest hop route to the destination. (For example, refer to ‘Proceedings of the 2nd IEEE Workshop on Mobile computing Systems and Applications, pages 90-100, February 1999’ in “Ad Hoc On-Demand Distance-Vector Routing” attributed to C. Perkins and E. Royer,).
The AODV method, used when transmitting data to a radio communication device of a certain destination and in the case where there is no existing valid route, starts a route discovery process and broadcasts a route request message which includes its own sequence number, a destination sequence number which it has, and a route request message identifier. When the adjacent radio communication device does not have sufficiently new route information on the route to the destination radio communication device, the adjacent radio communication device establishes a route in the reverse direction to the radio communication device which has transmitted the received route request message, and broadcasts the same route request message. However, a route request message which had already been received is not broadcast is. The destination radio communication device or the radio communication device which has sufficiently new route to the destination transmits a route reply message which stores the current sequence number of the destination radio communication device to the radio communication device which is the source of the route request message by unicasting. The radio communication device which has received the route reply message updates its route information based on information in the route reply message and forwards the route reply message to the radio communication device which has made the route request message using the route in the reverse direction if the sequence number of the destination is the newest one or if the sequence number is the same but the hop count to the destination is small. When the route reply message arrives at the radio communication device which has made the route request message, the route to the destination radio communication device is established.
A method not applying the route based on the shortest hop count is disclosed, in which radio communication devices adjacent to each other set a bit-error rate and forwarding speed, and based on them, the weighting of a link is calculated in each radio communication device and these link weights are added to the route request message, and then, the destination radio communication device selects the optimum route and responds to the message (for example, refer to JP-A-2003-152786).
However, in the conventional configuration, the route is established according to only the freshness of route information, determined from the sequence number, and the hop count, and therefore a radio communication device along the route which has insufficient battery remaining power happens to be selected. In this case, if the battery of the selected radio communication device is exhausted, the route becomes invalid and the route discovery procedure is performed in the ad hoc network again. Accordingly, there are problems that power consumption of all radio communication devices increases, and that throughput decreases due to the overhead increase in the communication band caused by control messages.
In another conventional configuration, since the weighing is calculated for the link between radio communication devices adjacent to each other, the search for neighboring radio communication devices and a link connection procedure are required when searching the route. Accordingly, there are problems that processing for each radio communication device increases and that the overhead increases because of signaling.